Unlinking objects from duplicated scene
I think your problem is the following one:

Unlink in the Outliner will unlink the object from its Collection, not from its duplications.

A linked duplication is a complete other thing than an object linked to a collection. To link-duplicate an object (make a copy that will follow all the modifications on the original), you need to press altD instead of shiftD.

To unlink a duplication, i.e. make it single user that won't depend on its linked duplications, select your object, go to the header menu > Object > Relations > Make Single User > Object &amp; Data, then select Selected Object.

The problem is that it will also unlink from the objects of the same scene (maybe there's a way not to but I don't know it).